#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int MOD = 1e9 + 7;
const int N = 2010;

int gcd(int a, int b)
{
    return b ? gcd(b, a % b) : a;
}

ll qui(ll a, ll b)
{
    ll res = 1;
    while (b)
    {
        if (b & 1)
            res = res * a % MOD;
        b >>= 1;
        a = a * a % MOD;
    }
    return res;
}

ll fac[N], inv_fac[N];
ll S[N][N];

void init()
{
    fac[0] = 1;
    for (int i = 1; i < N; i++)
        fac[i] = fac[i - 1] * i % MOD;
    inv_fac[N - 1] = qui(fac[N - 1], MOD - 2);
    for (int i = N - 1; i > 0; i--)
        inv_fac[i - 1] = inv_fac[i] * i % MOD;
    S[0][0] = 1;
    for (int i = 1; i < N; ++i)
    {
        for (int j = 1; j < N; ++j)
        {
            S[i][j] = (j * S[i - 1][j] % MOD + S[i - 1][j - 1]) % MOD;
        }
    }
}

ll comb(int a, int b)
{
    return fac[a] * inv_fac[b] % MOD * inv_fac[a - b] % MOD;
}

struct custom_hash
{
    static uint64_t splitmix64(uint64_t x)
    {
        x ^= x << 13;
        x ^= x >> 7;
        x ^= x << 17;
        return x;
    }
    size_t operator()(uint64_t x) const
    {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count(); // 时间戳
        return splitmix64(x + FIXED_RANDOM);
    }
};

void solve()
{
    ll n, x;
    cin >> n >> x;
    int mx = 0;
    vector<ll> a(n);
    map<ll, ll> mp1, mp2;
    priority_queue<ll, vector<ll>, greater<ll>> heap1, heap2;
    ll t = 0;
    for (int i = 0; i < n; i++)
    {
        cin >> t;
        // mp1[t ^ x] ++;
        // mp2[t] ++;
        heap1.push(t);
        heap2.push(t ^ x);
    }
    for (int i = 0; i < n - 1; i++)
    {
        if (i & 1)
        {
            while (mp2[heap1.top()])
            {
                mp2[heap1.top()]--;
                heap1.pop();
            }
            ll tt = heap1.top();
            // cout << tt << endl;
            mp1[tt ^ x]++;
            heap1.pop();
        }
        else
        {
            while (mp1[heap2.top()])
            {
                mp1[heap2.top()]--;
                heap2.pop();
            }
            ll tt = heap2.top();
            mp2[tt ^ x]++;
            heap2.pop();
        }
    }
    if (n & 1)
    {
        while (mp2[heap1.top()])
        {
            mp2[heap1.top()]--;
            heap1.pop();
        }
        cout << heap1.top() << endl;
    }
    else
    {
        while (mp1[heap2.top()])
        {
            mp1[heap2.top()]--;
            heap2.pop();
        }
        cout << heap2.top() << endl;
    }
}

int main()
{
    // cout << (114514 ^ 1919810);
    int t;
    cin >> t;
    while (t--)
        solve();
    return 0;
}